An anisotropically conductive sheet is a sheet exhibiting conductivity only in its thickness-wise direction or having pressure-sensitive conductive conductor parts exhibiting conductivity only in its thickness-wise direction when it is pressurised in the thickness-wise direction. Since the anisotropically conductive sheet has features that compact electrical connection can be achieved without using any means such as soldering or mechanical fitting, and that soft connection is feasible with mechanical shock or strain absorbed therein, it is widely used as a connector for achieving electrical connection between a circuit device, for example, a printed circuit board, and a leadless chip carrier, liquid crystal panel or the like in fields of, for example, electronic computers, electronic digital clocks, electronic cameras and computer key boards.
On the other hand, in electrical inspection of circuit devices such as printed circuit boards and semiconductor integrated circuits, it is conducted to cause an anisotropically conductive elastomer sheet to interpose between an electrode region to be inspected of a circuit device, which is an inspection target, and an electrode region for inspection of a circuit board for inspection in order to achieve electrical connection between electrodes to be inspected formed on one surface of the circuit device to be inspected and electrodes for inspection formed on the surface of the circuit board for inspection.
As such anisotropically conductive elastomer sheets, there have heretofore been known those of various structures.
For example, as anisotropically conductive elastomer sheets exhibiting conductivity under an unpressurised state, there have been known those in which conductive fibers are arranged in a sheet base composed of insulating rubber in a state oriented so as to extend in a thickness-wise direction of the sheet, those in which conductive rubber incorporating carbon black or metal powder and insulating rubber are alternately laminated along a plane direction (see Japanese Patent Application Laid-Open No. 94495/1975), etc.
On the other hand, as anisotropically conductive elastomer sheets exhibiting conductivity in a state pressurised in the thickness-wise direction thereof, there have been known those obtained by uniformly dispersing metal particles in an elastomer (see Japanese Patent Application Laid-Open No. 93393/1976), those obtained by unevenly distributing particles of a conductive magnetic material in an elastomer to form many conductive path-forming parts extending in the thickness-wise direction thereof and insulating parts for mutually insulating them (see Japanese Patent Application Laid-Open No. 147772/1978), those with a difference in level defined between the surface of conductive path-forming parts and insulating parts (see Japanese Patent Application Laid-Open No. 250906/1986), etc.
In recent years, however, a sheet capable of holding charge in its surface under an unpressurised state, and moving the charge held in the surface in a thickness-wise direction thereof when pressurised in the thickness-wise direction, thereby controlling the quantity of the charge at the surface is required in fields of electronic parts and electronic part-applied instruments.
However, the conventional anisotropically conductive elastomer sheets do not sufficiently satisfy such properties.